Telechelic telomers of chlorotrifluoroethylene

ABSTRACT

Iodine terminated liquid telechelic telomers of chlorotrifluoroethylene (CTFE) containing an average of more than 1 CTFE unit per molecule are novel compounds. The telomers can be prepared by a photochemically initiated reaction between liquified CTFE and either elemental iodine or the telogen ICF 2  CFClI at temperatures below about 50° C.

This is a continuation of application(s) Ser. No. 07/992,345 filed onAug. 5, 1993 now abandoned which is a divisional of Ser. No. 07/745,308,now U.S. Pat. No. 5,262,025 filed Aug. 15, 1991.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to telomers of chlorotrifluoroethylene. Moreparticularly, this invention relates to novel iodine-terminatedtelechelic telomers of chlorotrifluoroethylene that are prepared fromelemental iodine and chlorotrifluoroethylene.

2. Background Information

Bifunctional or telechelic telomers derived from fluorinated olefins areknown and are becoming increasingly important based on their desirableproperties, particularly insolubility in organic liquids and thermalstability. For example, telomers of tetrafluoroethylene prepared byreacting ICF₂ CF₂ I with CF₂ =CF₂ are reported by V. Tortelli and C.Tonelli in the Journal of Fluorine Chemistry [43 (1990), p. 199].

Addition reaction products of chlorotrifluoroethylene (CTFE) withfluorine, chlorine, bromine and the interhalogens BrF, IF, ICl, and IBrare reported and have been well characterized in the chemicalliterature. These products have been prepared by heating or the use offree radical initiators such as peroxides. Photochemical initiation ofthe reactions is not reported.

The reaction of chlorotrifluoroethylene with elemental iodine isreported by J. T. Barret al. (J. Amer. Chem. Soc., 1951, 73, 1352. Amixture containing equal weights of the reactants was sealed in a glasstube and allowed to stand for several days under ambient conditions. Theresultant liquid product, thought to be1-chloro-1,2,2-trifluoro-1,2-diiodoethane, was distilled in 30-35% yieldand boiled from 54°-55° C. under a pressure of 20 mm Hg. The productdecomposed upon standing to yield iodine and no other isolatableproduct, and was not sufficiently stable to be analyzed. By comparison,the reaction product of chlorotrifluoroethylene with iodine monochloridewas stable and was characterized as CF₂ ClCFClI.

M. Hauptschein et al. [JACS 79, 2549 (1957)] describes the reaction ofchlorotrifluoroethylene with the stable telogen reported by Bart ,namely CF₂ ClCFClI, at a temperature of 200° C. using a spiral tubereactor that minimized contact time between the reactants. The productcontained 22 weight percent each of the telomers CF₂ ClCFCl(C₂ F₃Cl)_(n) I where the value of n was 1, 2, or 3 and 33 weight percent oftelomers wherein n was 4 or greater.

R. Haszeldine [J.C.S. 4291 (1955)] describes the telomerization ofchlorotrifluoroethylene in the presence of the telogen ClCF₂ CFClI andultraviolet light or heat to yield telomers. Telomers containing up to20 repeating units per molecule are characterized as liquids. The authorproposes using peroxides as the free radical source for large scalereactions.

The article by Haszeldine makes no mention of using the bifunctionaltelogen ICF₂ CFClI, reported as unstable in the aforementioned articleby Bart et al., to initiate the telomerization ofchlorotrifluoroethylene (CTFE). Based on the instability of this telogenreported by Bart et al. it is unlikely that one would considersubstituting it for the telogen ClCF₂ CFClI reported by Haszeldine.

The present inventor therefore considered it surprising to discover thatwhen iodine is combined with more than an equimolar amount of CTFE theiodine will react substantially completely in the presence ofultraviolet or visible radiation to initially produce the telogenreported by Barr et al. Upon further exposure to radiation the telogenis gradually converted to stable telomers represented by the generalformula I(CF₂ CFCl)_(n) I, where the average value of n is greaterthan 1. The value of n for a particular product is determined by thereaction conditions, specifically the type of radiation, exposure time,and the reaction temperature.

The bifunctional telomers of CTFE can be reacted with fluorine, olefinsor fluoroolefins to obtain products in the form of liquids, solids andgreases.

The present inventor also discovered that the bifunctional telogen ICF₂CFClI can be isolated if the reaction of CTFE and iodine is conducted inthe presence of visible light or gamma radiation. Contrary to theteaching of Bart et al. the telogen is stable when stored in the dark attemperatures below about 30° C.

SUMMARY OF THE INVENTION

Iodine terminated telechelic telomers of chlorotrifluoroethylene (CTFE)containing an average of more than one CTFE unit per molecule are novelcompounds. The telomers can be prepared by a photochemically initiatedreaction between CTFE and either iodine or the telogen ICF₂ CFClI attemperatures below about 50° C.

DETAILED DESCRIPTION OF THE INVENTION

This invention provides telechelic telomers of the average formula I(CH₂CH₂)_(q) (R¹)_(m) (CF₂ CFCl)_(n) (R¹)_(p) (CH₂ CH₂)_(q) I, where R¹ isselected from the group consisting of fluoroalkylene radicals containingfrom 2 to 5 carbon atoms and radicals of the formula--CF2CF(ORf)--whereRf represents a perfluoroalkyl radical containing 1 or 2 carbon atoms,the average value of n is greater than 1 and the average values of m, pand q are individually 0 or a positive number.

This invention also provides a method for preparing an iodine terminatedtelechelic telomar of chlorotrifluoroethylene, said method comprisingthe steps of

1) exposing a mixture of elemental iodine and a stoichiometric excess ofliquified chlorotrifluoroethylene to visible or ultraviolet light whilemaintaining said mixture at a temperature of from 20° to 50° C. for aperiod of time sufficient to prepare a telomar containing an average ofmore than one chlorotrifluoroethylene unit per molecule, and

2) isolating said telomar from the mixture.

Alternatively, the iodine can be replaced by the telogen ICF2CFClI. Thetelogen can be prepared by reacting elemental iodine with CTFE under thesame conditions used to prepare the present telomers, but for shorterperiods of time. The telogen can also be prepared by exposing a mixtureof iodine and CTFE to gamma radiation.

The present invention is based on the unexpected ability of elementaliodine and a stoichiometric excess of chlorotrifluoroethylene, referredto hereinafter as CTFE, to react in the presence of visible orultraviolet light to form stable telechelic telomers. The lightpreferably exhibits a wavelength within the range of from 300 to 800nanometers.

The present telomers are characterized as comprising 1) an average ofmore than 1 repeating unit per molecule derived from CTFE, and 2) aniodine atom at each of the two terminal positions. The term "telechelic"refers to the bifunctional nature of the present telomers resulting fromthe presence of the two iodine atoms.

The average number of repeating units derived from CTFE, represented byn in the preceding formula, is greater than 1. This value can be as highas about 300, however this value is preferably from 2 to about 10, thispreference being based on the physical state of these telomers, whichare relatively high boiling liquids under ambient conditions oftemperature and pressure. Liquids are preferred for many end useapplications of CTFE telomers.

For some end use applications the properties of the presentiodine-terminated telechelic telomers derived from CTFE are modified byreacting the telomers with fluorine or with ethylenically unsaturatedfluorinated and/or non-fluorinated compounds such as ethylene,hexafluoropropene, tetrafluoroethylene and perfluorinated vinylalkylethers wherein the alkyl portion of the ether contains 1 or 2 carbonatoms. Preparation of Telechelic CTFE Telomers

The present telomers are obtained by the reaction of elemental iodinewith a stoichiometric excess of liquified CTFE in the presence ofvisible or ultraviolet light. In the presence of excess CTFE theinitially formed telogen reacts to form the telomers of this invention.

The reaction of iodine and CTFE to form the telogen is an equilibriumthat can be represented by the equation 1

    CF.sub.2 =CFCl+I.sub.2 →ICF2CFClI                   (1)

The equilibrium constant for the reaction at room temperature is about0.22. Because the concentration of the iodine is limited by itsolubility in the reaction mixture, it is therefore necessary to usemore than the required stoichiometric amount of CTFE to drive thereaction toward formation of the desired telogen. The term"stoichiometric amount" with reference to equation 1 is one mole ofiodine per mole of chlorotrifluoroethylene.

At temperatures below about 0° C. the solubility of iodine in liquidCTFE becomes so low that the rate of conversion of iodine to the telogenis slowed. At temperatures above about 50° C. the equilibrium constant(K) for the reaction decreases.

The factors influencing the rate of telogen formation appear to be therate of solubilization of the iodine in the CTFE and the intensity ofthe radiation. Improving the distribution of the solid iodine throughoutthe reaction mixture is one means to increase the rate of solubilizationand hence the rate of telomar formation. This can be achieved byagitating the liquid CTFE using mechanical means or allowing the CTFE toboil by cooling the portion of the reactor occupied by vaporized CTFE.

Preferred conditions for preparation of the telogen are a reactiontemperature of from 20° to about 40° C. using a molar ratio of CTFE toiodine of from 6:1 to 30:1.

The exposure time required to convert substantially all of the iodine totelogen is at least partially dependent on the wavelength and intensityof the radiation to which the reaction mixture is exposed. Usingsunlight, exposure times of from about 100 to about 200 hours should besufficient. The course of the reaction can conveniently be followed byobserving the amount of unreacted iodine remaining in the mixture.

The use of ultraviolet light for formation of the telogen is preferredbased on the somewhat slower rate of this reaction in the presence ofvisible light. Because the rate of telogen formation is limited by thesolubilization rate of the iodine, from the viewpoint of energyconservation it may be desirable to first prepare the telogen in thepresence of visible light, particularly sunlight, and then employultraviolet light to react the telogen with additional CTFE to form thepresent telomers.

Because the rate of telomerization appears to be considerably slowerthan the rate of telogen formation when the reaction of iodine withexcess CTFE is carried out in the presence of visible light or gammaradiation from radioactive cobalt rather than ultraviolet radiation, byconducting the reaction under conditions less favorable for thetelomerization reaction it is possible to isolate the telogen in theabsence of substantial amounts of telomer.

When gamma radiation is used to initiate reaction of elemental iodineand CTFE, the telogen can be isolated in the absence of substantialamounts of telomar.

The reaction of the initially formed telogen with additional CTFE in thepresence of visible or ultraviolet radiation to form the presenttelomers can be represented by equation 2.

    ICF.sub.2 CFClI+nCF.sub.2 =CFCl→I(CF.sub.2 CFCl).sub.n+l I (2)

This does not appear to be an equilibrium reaction. The resultanttelomers are stable under conditions that decompose the telogen.

Depending upon the intensity of the radiation at the reaction mixtureand the desired degree of polymerization, represented by the value for nin the foregoing equation 2, the present inventors have found thatexposure times of from 48 to about 300 hours are sufficient to reactsubstantially all of the telogen. It appears that the average value of nincreases with longer exposure times.

Any convenient source of ultraviolet radiation can be used to preparethe telogens and telomers. Mercury vapor lamps exhibiting maximumradiation in the range from 250 to about 350 nm are preferred based ontheir cost and availability.

At wavelengths below about 300 nm the telomer partially decomposes toyield CF₂ =CF(CF₂ CFCl)_(n) I with the generation of ICl as aby-product. ICl will react with CTFE in the same manner as elementaliodine, however the resultant telomer may be less stable than thepresent telomers due to the presence of the ClCF₂ CFCl-- group that canundergo dechlorination. It is therefore preferable to use reactorsformed from Pyrex(R) glass rather than quartz, based on the ability ofquartz and the inability of Pyrex glass to transmit wavelengths ofradiation below about 300 nm.

The wavelength range of from 300 to about 500 nm. appears optimum withregard to accelerating the rate at which the telogen ICF2CFClI reactswith CTFE to form the present telomers while avoiding decomposition ofthe telomer.

Subsequent Reaction of the CTFE Telomer With Fluorine or Olefins

For certain end use applications the presence of terminal iodine atomsand/or a unit derived from CTFE is undesirable. Replacement of theiodine atoms with fluorine can be achieved by reacting the telomer withelemental fluorine. A substantially quantitative replacement of theiodine atoms occurs when fluorine is bubbled through the liquid telomerat a temperature of from 0° C. to about ambient. Telomers containing 9or fewer repeating units yielded liquid fluorinated products. Under thesame reaction conditions higher molecular weight telomers formedgreases.

The present telomers react with fluorinated ethylenically unsaturatedorganic compounds such as tetrafluoroethylene (TFE),1,1-difluoroethylene, and perfluorinated alkylvinyl ethers attemperature of from about 150° to about 250° C. The alkyl portion of theperfluorinated ethers preferably contains 1 or 2 carbon atoms. The--CFClI terminal group (a) of the telomer appears considerably morereactive with these fluorinated compounds than the ICF₂ -- terminalgroup (b).

The present inventors found that after 16 hours of reaction at 165° C.82% of the telomer reacted with TFE to yield I(CF₂ CFCl)_(n) CF₂ CF₂ I.

At a temperature of 220° C. 90% of the (a) terminal groups reacted toform I(CF₂ CFCl)_(n) (CF₂ CF₂)_(m) I, where the value of m is about 1.4,indicating the reaction of more than one molecule of tetrafluoroethyleneper molecule of telomer.

Tetrafluoroethylene is known to react with iodine terminatedfluorocarbon telomers to yield copolymers containing from about 10 toabout 300 or more units derived from this monomer. These copolymersrange in viscosity from viscous oils to greases to solid materials.

Hexafluoropropene reacts with the present telomers at a slower rate thantetrafluoroethylene (TFE) and other fluorinated ethylenicallyunsaturated compounds. As with TFE, reaction at terminal group (a) wasfavored.

Both the present CTFE telomers and reaction products of these telomerswith perfluorinated ethylenically unsaturated compounds will react withethylene or other ethylenically unsaturated hydrocarbons in the presenceof a platinum catalyst. The reaction product of one mole of telomer withtwo moles of ethylene exhibits the formula

    ICH2CH2(CF2CFCl)n( CH2CH2I)

In one experiment 44% of terminal group (a) and 22% of terminal group(b) reacted after 19 hours at 70° C. It is believed that the incompletereaction was caused by elemental iodine poisoning the platinum catalyst.Poisoning of the catalyst could be avoided by ensuring that all of theresidual telogen was removed from the reactor prior to reaction of thetelomer with ethylene.

Telomers containing hydrogen and chlorine on adjacent carbon atoms mayundergo dehydrochlorination when heated at temperatures above about 150°C. Because this reaction adversely affects the thermal stability andphysical properties of the resultant telomer, when the telomers arereacted, also referred to as "endcapped", with ethylene or other olefincontaining hydrogen on at least one of the ethylenically unsaturatedcarbon atoms, it is desireable to ensure the absence ofdehydrochlorination by first reacting the telomer with a perfluorinatedethylenically unsaturated compound such as hexafluoropropene ortetrafluoroethylene, and then reacting the resultant telomer with theolefin.

EXAMPLES

The following examples describe preferred embodiments of the presenttelomers and the method for preparing these telomers, and shouldtherefore not be considered as limiting the scope of the accompanyingclaims. Unless otherwise specified all parts and percentages are byweight.

Description of Equipment

One type of Carius tube (I) used for the telomerization reactions had acapacity of 2.4 ml and was prepared from 8.5 inch (21.6 cm) sections ofPyrex(R) glass tubing having an outside diameter of 8 mm and a wallthickness of 2.0 mm. A second type of Carius tube (II) had a capacity of75 ml, a length of 9 inches (22.9 cm) and was equipped with a TeflonRotoflow(R) valve. A third type of Carius tube was fabricated fromquartz.

The ultraviolet light sources were a model RPR-208 Rayonet(R) reactorequipped with either a low pressure 254 lamp (1), a medium pressure254-600 nanometer lamp (2) or (3) a 1000 watt Hanovia(R) medium pressuremercury lamp.

The telomers were characterized by gas liquid chromatography (GLC) usinga 15 meter SE-30 column, 10 psi (69 kPa) of back pressure and atemperature profile of 5 minutes at 40° C. followed by an increase of10° C./minute to 270° C.

Some of the telomers were characterized using a Brinker ¹⁹ F nuclearmagnetic resonance spectrometer operating at a frequency of 235megahertz.

Example 1

This example demonstrates the preparation of telomers by the irradiationwith ultraviolet light of mixtures containing various proportions ofelemental iodine and chlorotrifluoroethylene (CTFE). The quantities ofiodine and CTFE listed in Table 1 were sealed in a type I or type IICarius tube and irradiated with one of the three ultraviolet lightsources for the time period specified in Table 1. The tube was thenopened and the unreacted CTFE recovered and weighed. The liquidremaining in the tube was then analyzed using GLC and ¹⁹ F nuclearmagnetic resonance to determine the relative concentrations of thevarious telomers present. The results of these analyses are summarizedin Table 1.

                                      TABLE 1                                     __________________________________________________________________________    Sample                                                                            g. charged/g.                                                                        recovered                                                                           Mole                                                                              Conditions                                                                             Prod.                                                                             n =                                         No. CTFE   I.sub.2                                                                             Ratio                                                                             UV Source/Hrs.                                                                         Wt. (g)                                                                           1/2/3/4                                     __________________________________________________________________________    1   44.3/41.5                                                                            4.64/0                                                                              20  1/48     7.3 1.5/1/tr/0                                  2   65.5/53.91                                                                           52.8/26.5                                                                           2.7 3.sup.b /72                                                                            37.5                                                                              30/1/0/0                                    3   62.7/52.6                                                                            10.9/0                                                                              13  1/168    20.5                                                                              1.6/1/0.7/tr.sup.a                          4   64.3/ND                                                                              19.9/1.3                                                                            7   1/156.sup.c                                                                            40.2                                                                              2.1/1/0.56/0.32                             5   59/43.2                                                                              26.1/5.9                                                                            4.9 2/288    34.6                                                                              2.1/1/0.6/0.3                               6   39.24/ND                                                                             10.17/0                                                                             8.4 1/200    16.6                                                                              4/1/0.7/tr/tr                               7   58.9/39.6                                                                            21.2/0                                                                              6.1 3.sup.d /160                                                                           39.5                                                                              4.6/1/tr                                    __________________________________________________________________________     .sup.a tr = trace                                                             .sup.b Air circulation reduced power reaching sample to 100 watts.            .sup.c Sample beated at 40° C. throughout exposure period              .sup.d Sample exposed using a quartz Carius tube                              ND Not determined                                                        

Example 2

This example demonstrates the ability of lower molecular weight telomersprepared by irradiating mixtures of CTFE and iodine with ultravioletlight to be separated into low and high molecular weight fractions. Aportion of the liquid telomar prepared as sample 3 in Example 1 wasplaced under high vacuum (0.05 mm Ha) for three hours. The residueexhibited a consistency between that of a liquid and a grease and wasconsiderably more viscous than the initial sample 3. Analysis of theproduct by gas chromatography and ¹⁹ F NMR indicated an average of 4CTFE units per molecule.

Example 3

This example demonstrates the ability of an iodineterminated telogen ofCTFE to undergo reaction with additional CTFE in the presence ofultraviolet light to form telomers.

A mixture of 124.46 g (1.07 moles) of CTFE and 72.68 (0.29 mole) ofiodine was placed in a Carius tube. The tube was then sealed and rotatedend-over-end for five days close to a source of gamma radiation. Thetube was then opened and 102.58 g (0.88 mole) of CTFE were recoveredtogether with 45.7 g of a purple liquid. Analysis using gas liquidchromatography indicated that the liquid was substantially pure telogen,ICF₂ CFClI (0.12 mole), containing a small amount of dissolved iodine.

A glass Carius tube was charged with 4.63 g (12.5 mmol) of the telogenand 39.9 (342 mmol) of CTFE. The tube was then sealed and irradiated forthree days under the full power of the ultraviolet light generated by a1000 watt Hanovia(R) medium pressure lamp. The tube was then opened and34.33 g of CTFE were recovered together with 7.67 g of a liquid and 2.42g of a solid residue that was subsequently shown to be mostly iodine.Analysis using ¹⁹ F NMR indicated that the liquid product was a telomercontaining an average of 5.0 CTFE units per molecule.

In a similar experiment 58.7 g of CTFE and 14.9 g of iodine (mole ratioof CTFE to iodine=8.6) was exposed to full sunlight for seven days, atwhich time all of the iodine appeared to have dissolved. The resultantcolored solution was then irradiated at a distance of about 25 cm from a1000 watt medium pressure mercury vapor lamp for seven days, at whichtime the color of the initial solution was fading. 20.4 g of CTFE wasrecovered together with 56.2 g of a viscous purple liquid.

The ¹⁹ F nuclear magnetic resonance spectrum was consistent with atelomer containing an average of 6.0 CTFE units per molecule.

Example 4

This example demonstrates the inability of hexafluoropropene to undergoa reaction with elemental iodine in the presence of ultraviolet light.

Iodine (0.19 g, 0.7 mmol) and hexafluoropropene (1.81 g, 12 mmol) weresealed into a Pyrex Carius tube. The tube was then rotated end-over-endat a distance of approximately 30 cm from a 1000 watt medium pressuremercury lamp for 42 hours. At the end of this time the tube containediodine and a free-flowing liquid that evaporated completely underambient conditions when the tube was opened. The liquid was assumed tobe unreacted hexafluoropropene.

Example 5

This example demonstrates the ability of chlorotrifluoroethylene totelomerize in the presence of iodine and sunlight.

A 75 cc-capacity Carius tube was charged with 14.8 g. of iodinecrystals. After being evacuated using a vacuum line while being cooledto -78 degrees C., the tube was charged with 61.5 grams ofchlorotrifluoroethylene. The tube was then sealed, removed from thevacuum line and exposed to full sunlight for 14 days. At the end of thisexposure period the tube contained a viscous liquid and no iodinecrystals. The tube was then opened and the contents allowed to flow intoa container. 9.0 grams of chlorotrifluoroethylene evaporated, leaving66.1 g. of a transparent pink grease that converted to a flowable oil at42 degrees C. This was equivalent to an 85% conversion of the initialchlorotrifluoroethylene.

Based on the ¹⁹ F nuclear magnetic resonance spectrum the product wasassigned the average formula I (CF2CFCl)₈.26 I. This spectrum exhibitedmaxima at the following chemical shifts: 49-54 ppm=m, 2.45 F; 65-71ppm=m, 0.77 F; 96-104 ppm=m, 2.2 F; 105-11 ppm=m, 18.3 F; 115-122 ppm=m,1.2 F; and 123-130 ppm=m, 6.5 F.

That which is claimed is:
 1. A telechelic telomer of the average formulaI(R¹)_(m) (CF₂ CFCl)_(n) (R¹)_(p) I where R¹ is selected from the groupconsisting of --(CF₂ CF(CF₃)--, --CF₂ CF₂ -- and CF₂ CF(ORf), where Rfis a perfluoroalkyl radical containing 1 or 2 carbon atoms, the averagevalue of n is from 2 to 10 and the average values of m and p areindividually 0 or a positive integer.
 2. A telechelic telomer accordingto claim 1 wherein the average value of n is from 5 to 10, inclusive andthe sum of m and p is from 1 to 4, inclusive.